This invention relates to a printing head apparatus for use with an impact dot printer and a manufacturing method of such an apparatus.
A printing head apparatus used with an impact dot printer is generally constructed as shown in FIG. 1. When a solenoid is excited, an armature 3 swings toward a core 1 by magnetic attraction with one end of said armature 3 used as a fulcrum. One end of a printing wire 4 is fitted to the other end of the armature 3. Dot printing is carried out when the printing wire 4 is moved by the actuation of the armature 3, and the other end of said printing wire 4 pushes an ink ribbon onto a sheet of paper (not shown). When the exciting force of the solenoid 2 is released, the armature 3 returns to its original position by the repulsive force of a return plate spring 5. This return plate spring 5 is fixed at one end, and imparts a returning force to the armature 3 by means of a collar 6 acting as a spacer for the armature 3. The collar 6 is generally made of a metal, for example, stainless steel, in the form of a cylinder, and interposed between the armature 3 and return plate spring 5 with the collar 6 being penetrated by the printing wire 4.
An exemplary arrangement of the printing head apparatus of FIG. 1 is shown in FIG. 2. A plurality of printing wires corresponding to the number of printing dots to be impressed on a sheet of paper are arranged in a circular form. The plural printing wires 4 are guided at their other end toward a sheet of paper (not shown) by a plurality of guides 10. The plural guides 10 are held in a prescribed housing 11. The printing wires 4 pass through holes 12 of corresponding return plate springs 5. The return plate springs 5 correspond in number to that of the printing wires 4 and are fixed to a plate spring holder 13 in a circular form. The armature 3 fitted to the printing wire 4 is magnetically attracted toward the core 1 by exciting the solenoid 2 which is set between the core 1 and plate spring holder 13. The solenoid 2 is constructed by winding a coil 15 around an iron core 14. When the excitation of the solenoid 2 is released, the armature is returned to its original nonprinting position by the repulsive force of the return plate spring 5, as previously described. The returned armature 3 is retained at a prescribed position by a stopper 16 made from, for example, synthetic resin or rubber. The stopper 16 is mounted on the inner wall of a rear case 17, which forms a housing of the printing head apparatus.
The structural section (a dotted circle 7 of FIG. 1) of the aforementioned printing head apparatus, which includes armature 3, printing wire 4 and collar 6 assembly, is particularly important to the operation of the printing head apparatus. As seen from FIG. 3 (which is a partial, enlarged view of FIG. 1 omitting plate spring 5), the structural section 7 is constructed by joining one end of the printing wire 4 to one end of the armature 3 with brazing material 10 such as silver or copper. The collar 6 penetrated by the printing wire 4 is welded at one end to the armature 3 by means of adhesive (i.e., not brazing materials). However, the conventional printing head apparatus constructed as described above has the drawbacks that the components of the apparatus are assembled by materials of different qualities such as the brazing material 10 and the adhesive agent. As seen from FIG. 4 (an enlarged cross sectional view of FIG. 3), the armature 3 and printing wire 4 are held together by an extremely small portion of the brazing material 10, thereby resulting in a decline in the mechanical strength of the abovementioned structural section 7. Further, said structural section 7 is manufactured by a plurality of steps, that is, the brazing of the components and their joining by adhesive, leading to an increase in the number of steps of manufacturing the printing head apparatus, and consequently in the cost thereof.